Ganciclovir is a synthetic guanine derivative which interferes with the replication of viruses, including cytomegalovirus (CMV). The drug is effective for both treatment and chronic suppressive therapy of CMV infections in a variety of patients. The Food and Drug Administration has recentlyapproved an oral form of ganciclovir as an alternative to parenteral drug in immunocompromised patient with CMV retinitis for chronic suppressive therapy. There are several pediatric patient groups who may benefit from use of oral ganciclovir. The purpose of our study is to obtain pharmacokinetic data by determining the absorption profile and achievalbe serum concentrations in children.